Animated Solution for Chemistry - Chemical Kinetics: Rate of a reaction can be expressed by Arrhenius equation as $k=A{e}^{-E/RT}$. In this equation, $E$ represents

The Arrhenius equation is one of the most elegant and fundamental relationships in chemical kinetics. It beautifully connects the macroscopic world of reaction rates with the microscopic world of molecular collisions and energies. The equation is given by:

Here, $k$ is the rate constant, $A$ is the pre-exponential factor (related to the frequency of collisions), $R$ is the universal gas constant, and $T$ is the absolute temperature. But the star of the show is $E$, which represents the Activation Energy ($E_a$).

Imagine you are trying to roll a heavy boulder up a hill to get it to the other side. If you don't push it hard enough, it will just roll back down. The height of that hill is analogous to the activation energy, $E$. It is the minimum extra amount of energy that reacting molecules must possess to break their old bonds and form new ones.

To truly understand this, we look at the Maxwell-Boltzmann distribution curve. This curve plots the fraction of molecules against their kinetic energy. In any gas or liquid, molecules are zipping around at different speeds. Some are slow, some are fast, and most are somewhere in the middle.

When we draw a vertical line on this graph at the value of $E$ (or $E_a$), we divide the molecules into two distinct groups:

1. The Reacting Molecules: The shaded region to the right of $E_a$ represents the fraction of molecules that have kinetic energy equal to or greater than the activation energy. When these high-energy molecules collide with the proper orientation, they successfully react to form products.

2. The Non-Reacting Molecules: The vast majority of molecules lie to the left of the $E_a$ line. These molecules simply do not have enough kinetic energy. When they collide, they just bounce off each other elastically, like billiard balls, without any chemical reaction taking place.

Therefore, the term $E$ in the Arrhenius equation precisely defines the threshold. It is the energy below which colliding molecules will not react. Any collision involving molecules with energy less than $E$ is an ineffective collision.